PMOS and NMOS transistors are common circuit components in many integrated circuits. Such transistors have a source and drain region formed in a semiconductor body, with a channel region residing therebetween. A gate electrode is formed over the channel. Upon proper biasing of the gate electrode and the source/drain regions, the transistors may be selectively controlled. For example, in some instances the transistors are turned completely on or off, wherein the transistors operate as switches. Alternatively, such devices can also be partially activated, wherein such devices operate as variable resistors.
The gate electrode is formed of a conductive material and overlies a gate dielectric. Based on the thickness of the gate dielectric, the drive current of the device can be influenced. Generally speaking, for a given gate dielectric, as its “effective oxide thickness” (EOT) increases, its drive current decreases, and as its EOT decreases, its drive current increases.
When polysilicon is employed as the gate electrode for transistor devices, the polysilicon is often doped to reduce its resistivity. If the dopant does not diffuse all the way down to the underlying dielectric interface, a poly depletion effect occurs, which results in an increase in the transistor EOT.
It is desirable to provide improvements in transistor fabrication.